The amount of power needed to move a vehicle over land or through the air increases with the speed of the vehicle, due to aerodynamic drag. The amount of power necessary to overcome aerodynamic drag directly translates into increased fuel consumption, and thus cost of operation.
Because of this, attention has been directed at reducing the aerodynamic drag of a wide variety of transport vehicles, such as trucks. The form drag of a truck is related in part to the shape of the frontal parts, such as the cab and the abruptness of its transition to the trailer or container. Typically, such forms are referred to as bluff bodies. The term bluff body relates to an aerodynamic definition for a particular geometry which lacks a streamlined shape. A bluff body has the characteristics that the bluff body contains, when placed in an air stream in a cross-section, an abrupt transition zone for the passing air stream. The abrupt transition zone causes drag.
There have been a variety of improvements made to improve the aerodynamic shape of these parts, such as by making the hood, windscreen, fenders etc. more streamlined in form, as well as by adding fairings to the cab roof, or the front of the truck box.
Another significant contributor to the form drag of a truck is the drag associated with the rear of the trailer. A typical trailer box will terminate with a large rectangular surface. This shape causes an area of reduced pressure to be created behind the trailer box as it moves over the highway, the result of which is to generate a retarding force that must be overcome with additional engine power, and thus additional fuel. Such shapes as the typical trailer box are also referred to as bluff bodies.
Accordingly, there have been efforts directed at adding a drag reducing device as a rear fairing to the rear of such a bluff body to lessen the reduced pressure area created at the rear, and thus improve the over the road fuel efficiency. However, the business of trucking is highly competitive and sensitive to operating costs, which include not only fuel costs but also capital costs and costs associated with any tasks that the driver or others must do to operate the truck and performing loading and unloading operations. In this regard, a rear fairing covering the back of the trailer box will typically also cover the loading/unloading doors. Therefore, such a rear fairing is cumbersome if permanently mounted to the trailer box. Likewise, dismounting and securing the rear fairing each time a loading/unloading operation is to be performed takes extra time, may require additional equipment to assist in the movement, stowage and positioning of the relatively large drag reducing device, and may not be within the skills of the driver and/or loaders.
Attempts have also been made to make the drag reducing device in some way retractable so that it does not impair off-highway activities. However, these efforts have to date not yielded devices having widespread use. There is therefore still a need for a rear fairing for transportation vehicles comprising bluff bodies, such as railroad carriers, busses, trucks and truck trailer boxes, which ably accommodates both aerodynamic and ease of use considerations to provide the user sufficient increased profitability to warrant its use.
From U.S. Pat. No. 5,498,059 such a drag reducing apparatus is known which attributes to this need. The drag reducing apparatus comprises a top panel and a side panel. The top panel is rotatably secured to a vehicle body to permit the top panel to assume a first collapsed configuration adjacent the vehicle body and a second position extended away from the vehicle body. The side panel is rotatably secured to a vehicle body to permit the second panel to assume a first collapsed configuration adjacent the vehicle body and a second extended configuration extended from the vehicle body. The top and side panels are joined together to permit the top and side panels to fold approximately together when the top and side panels are adjacent the vehicle body. The top panel comprises two joined panel sections to permit the top panel to be folded when in the first collapsed configuration and unfolded when in the second extended configuration.